The link between electrolytes and metals

doi:10.1126/science.abb9717

GSTDTAP > 气候变化

DOI	10.1126/science.abb9717
	The link between electrolytes and metals
	Christine M. Isborn
	2020-06-05
发表期刊	Science
出版年	2020
英文摘要	Solutions of alkali metals in liquid ammonia have fascinated scientists for more than 200 years. The “fine blue colour” of a dilute solution indicative of solvated electrons was first noted by Sir Humphry Davy in 1808 [([ 1 ][1]), p. 63] and independently published by W. Weyl in 1864 ([ 2 ][2]). A bronze sheen as the solution becomes highly concentrated (see the figure) develops as these solvated electrons coalesce into a metallic continuum. Charles Kraus, an early pioneer of the study of these solutions ([ 3 ][3]), noted that “these solutions…constitute a link between electrolytes, on the one hand, and metals, on the other” [([ 4 ][4]), p. 83]. On page 1086 of this issue, Buttersack et al. ([ 5 ][5]) combine low-temperature x-ray photoelectron spectroscopy with high-level simulations to reveal the energetics of metal-ammonia solutions across a large concentration range. These studies provide the missing energetic link to characterize the journey of solvated electrons from electrolyte to metal. ![Figure][6] A fascinating color change Alkali metal-ammonia solutions change from blue to bronze as the concentration of the metal is increased. This color change marks the shift of the solution from electrolyte to metallic. The photoelectron spectroscopy experiments by Buttersack et al. across the concentration range show how the electron gradually changes from localized to metallic. GRAPHIC: C. BICKEL/ SCIENCE Electrons are usually either relatively localized in atomic or molecular orbitals or can be delocalized in the energy bands of extended solids. For the much less common case of solvated electrons—which exist in a number of solvents, including water, but are most stable in ammonia—questions remain about the extent of localization and the degree of association with the parent ions and surrounding solvent. The solvent environment may change to support these species, and as the concentration increases, the electrons may interact to become spin-paired dielectrons and ultimately coalesce into a metallic state. These questions have motivated many studies of hydrated and ammoniated electrons over the years ([ 6 ][7], [ 7 ][8]). One of the most effective techniques for studying electronic energy levels is photoelectron spectroscopy, which measures the kinetic energy of electrons emitted after a substance is irradiated with light (based on the principles of the photoelectric effect), revealing electronic binding energies. This technique has been used to characterize hydrated electrons and ammoniated electrons, albeit at low concentrations, well below the electrolyte-to-metal transition. The development of a new apparatus enabled the application of x-ray photoelectron spectroscopy to a liquid ammonia microjet ([ 8 ][9]), allowing Buttersack et al. to collect the photoelectrons from the volatile, polar refrigerated metal-ammonia solution across the wide concentration range of 0.012 to 9.7 mol % metal. Over this range, the solution color changes from a lighter to a deeper blue and finally develops a bronze metallic sheen. The photoelectron spectra reveal the onset and growth of a peak beginning at a concentration of 0.08 mol % metal (see the figure). The energy of this peak is independent of the identity of the alkali metal in the solution, which suggests that the peak arises only from the ammoniated electron and that the metal parent ion does not play a direct role in this transition. As the concentration of the alkali metal increases, this peak gradually grows into a metallic conduction band with a sharp Fermi edge, and an additional plasmon peak appears. This plasmon peak is responsible for the characteristic bronze color of the metallic solution. This gradual transition is in contrast to the sharp transition proposed in recent work on metal-ammonia nanodroplets ([ 9 ][10]), which shows that the bulk liquid and small solvent clusters support different solvated electron structures at higher concentrations and therefore different metallic onsets. Modeling by Buttersack et al. complements the photoelectron spectroscopy data. They apply a metallic free-electron gas model to fit the growth of the conduction band and the sharp Fermi edge in the photoelectron spectra as the solution undergoes the electrolyte-to-metal transition. These metallic spectral features begin to reveal themselves at concentrations lower than when the solution begins to visually appear metallic bronze. On the dilute side of the concentration range (only one solvated electron or one solvated dielectron), ab initio molecular dynamics provide structures of the electron and dielectron solvated by ammonia molecules. These structures are then used for high-level vertical dissociation energy computations. Performing ab initio molecular dynamics of an excess electron or dielectron in bulk ammonia is a substantial computational feat and advances the field beyond previous static cluster calculations to reveal a diffuse ammonia solvation shell that is similar for both the electron and the dielectron. The spin densities suggest that the ammoniated electron resides within a cavity that is less structured than that of the hydrated electron. The high-level vertical dissociation energy calculations show that the energies to ionize the electron and the dielectron both fall within the measured photoelectron signal. With greatly increased computational resources, ab initio molecular dynamics simulations could be expanded to a larger scale to include metal ions dissolved in ammonia at a variety of concentrations. Studies such as these may be necessary to resolve some of the remaining controversy of the localized versus delocalized nature of the hydrated and ammoniated electron ([ 10 ][11]–[ 13 ][12]). These results would provide additional atomistic and electronic details of the electrolyte-to-metal transition. For now, the spectroscopic studies by Buttersack et al. provide the missing energetic and spectroscopic link and reveal the gradual transition to metallic behavior before our eyes can see it. 1. [↵][13]1. S. J. M. Thomas, 2. P. P. Edwards, 3. V. L. Kuznetsov , ChemPhysChem 9, 59 (2008). [OpenUrl][14][CrossRef][15][PubMed][16][Web of Science][17] 2. [↵][18]1. W. Weyl , Ann. Phys. 197, 601 (1864). [OpenUrl][19] 3. [↵][20]1. C. A. Kraus , J. Am. Chem. Soc. 43, 749 (1921). [OpenUrl][21] 4. [↵][22]1. C. A. Kraus , J. Chem. Educ. 30, 83 (1953). [OpenUrl][23] 5. [↵][24]1. T. Buttersack et al .,Science 368, 1086 (2020). [OpenUrl][25][Abstract/FREE Full Text][26] 6. [↵][27]1. M. T. J. H. Lodge et al ., J. Phys. Chem. B 117, 13322 (2013). [OpenUrl][28][CrossRef][29][PubMed][30] 7. [↵][31]1. E. Zurek, 2. P. P. Edwards, 3. R. Hoffmann , Angew. Chem. Int. Ed. 48, 8198 (2009). [OpenUrl][32][CrossRef][33][PubMed][34] 8. [↵][35]1. T. Buttersack et al ., J. Am. Chem. Soc. 141, 1838 (2019). [OpenUrl][36][CrossRef][37][PubMed][38] 9. [↵][39]1. S. Hartweg, 2. A. H. C. West, 3. B. L. Yoder, 4. R. Signorell , Angew. Chem. Int. Ed. 55, 12347 (2016). [OpenUrl][40][CrossRef][41][PubMed][42] 10. [↵][43]1. I. A. Shkrob , J. Phys. Chem. A 110, 3967 (2006). [OpenUrl][44] 11. 1. R. E. Larsen, 2. W. J. Glover, 3. B. J. Schwartz , Science 329, 65 (2010). [OpenUrl][45][Abstract/FREE Full Text][46] 12. 1. L. D. Jacobson, 2. J. M. Herbert , Science 331, 1387 (2011). [OpenUrl][47][Abstract/FREE Full Text][48] 13. [↵][49]1. C.-C. Zho, 2. E. P. Farr, 3. W. J. Glover, 4. B. J. Schwartz , J. Chem. Phys. 147, 074503 (2017). [OpenUrl][50] Acknowledgments: The author is supported by grants from the U.S. Department of Energy, Basic Energy Sciences, Computational and Theoretical Chemistry and Condensed Phase and Interfacial Molecular Science programs (DE-SC0019053 and DE-SC0020203). 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领域	气候变化 ; 资源环境
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引用统计
文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/273431
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Christine M. Isborn. The link between electrolytes and metals[J]. Science,2020.
APA	Christine M. Isborn.(2020).The link between electrolytes and metals.Science.
MLA	Christine M. Isborn."The link between electrolytes and metals".Science (2020).